A Study to Investigate the Long-Term Safety of ZX008 (Fenfluramine Hydrochloride) Oral Solution in Children and Adults With Epileptic Encephalopathy Including Dravet Syndrome and Lennox-Gastaut Syndrome

Inclusion Criteria: * Male or nonpregnant, nonlactating female * Satisfactory completion of a core study * Has a rare seizure disorder, such as epileptic encephalopathy and has successfully completed another Zogenix-sponsored clinical trials with ZX008 * Subject's caregiver is willing and able to be compliant with study procedures, visit schedule and study drug accountability Exclusion Criteria: * Current cardiac valvulopathy or pulmonary hypertension that is clinically significant * Moderate or severe hepatic impairment * Receiving monoamine oxidase inhibitors, serotonin agonists, serotonin antagonists, and serotonin reuptake inhibitors within 14 days of receiving ZX008